More Information

SR 520 Bridge - Why We Close It

The SR 520 Evergreen Floating Bridge is unique because of its length, location over water and age. The floating portion of the bridge spans approximately 7,700 feet. These factors make the bridge vulnerable to closures. As with any structure that moves or floats, the SR 520 Bridge has a full crew dedicated to its maintenance and repair.

The SR 520 Bridge is also a major commuter route connecting Seattle to the Eastside. Traffic has grown steadily since the bridge opened in 1963. Over 115,000 drivers now use the 520 bridge every day.

As a major east-west lifeline, our bridge crews closely monitor the forces of wind and water to keep the bridge in good condition. Our incident response teams and traffic engineers monitor the road condition to keep traffic flowing. Sometimes these incidents are large enough to require a full bridge closure, such as the December 14, 2006 windstorm. Due to the age of the bridge, we cannot rule out future storm closures until a new bridge is built.

Who makes the decision to close the bridge?

The SR 520 Bridge has a dedicated bridge staff that consists of seven fulltime technicians, one electrician and the bridge supervisor. At anytime this crew can decide to close the bridge to traffic. Though we would like to plan for every closure of the SR 520 Bridge, Mother Nature and traffic sometimes have whims of their own. A minimum of three people are on standby at all times in case of foul weather or other emergencies.

How do unplanned closures work?

We make every attempt to reduce disruption to drivers but in an emergency we have to close the bridge quickly. There are movable sections of concrete barrier on either end of the bridge to help us turn traffic around safely. WSDOT crews have a traffic control plan for emergency closures. We alert drivers to the closure by electronic signs at either end of the bridge and on highways that lead to the bridge. These signs remain illuminated during the duration of the closure and are turned off when the bridge re-opens to traffic.

What are the conditions for an unplanned emergency closure?

Wind

The criteria for closing the bridge to traffic and opening the draw span is 50 mph gusts sustained for 15 minutes. When a 40 mph gust is sustained for one minute, a warning alarm calls crews to the bridge for inspection and monitoring. As with all of our bridges our experienced crews can close the bridge at any time they deem it unsafe or when there is a potential for damage. Check the current wind speed.

Why does opening the bridge drawspan help in a windstorm?

Opening the drawspan relieves stress on the bridge structure. During a windstorm the force of the waves pushes north on floating span, twisting and rocking the structure. During this movement the bridge is vulnerable to damage. When the drawspan is opened some of the force is released allowing the bridge structure to relax.

Traffic incidents

Large accidents and Washington State Patrol activity can temporarily shut down the bridge. The WSDOT Incident Response Team has tow trucks nearby to quickly remove stalled vehicles and keep traffic moving during an incident.

Natural disasters

After a natural disaster such as an earthquake, we dispatch our bridge crews to inspect the bridge. These inspections may require us to close the bridge.

Threats

Any security threat to the bridge could result in an emergency closure. Our crews' priority is to keep drivers safe and protect the bridge.

Emergency repairs

After a high-wind incident, other natural disaster or a vehicle collision, the bridge may sustain damage that we need to fix immediately. Crews also will close the bridge if drivers are in danger.

How do planned closures work?

WSDOT puts together a traffic control plan for the closure. We select closure times to minimize the inconvenience to daily commuters of the bridge and to protect the bridge structure.

What are the conditions for a planned closure?

Routine Maintenance

Every month our experienced crews inspect the bridge to catch problems early and extend the life of the bridge. These closures are scheduled for the second Thursday of every month and typically occur between midnight and 5 a.m. During this time drivers can expect the bridge to be closed for up to 30 minutes at a time. While the bridge is closed, bridge crews test the working order of the drawspan, conduct other routine safety checks and do preventive maintenance. During these intermittent closures, drivers will not be diverted off SR 520. Drivers beyond Montlake or 92nd Avenue NE must wait up to 30 minutes for the bridge to reopen.

Scheduled Repairs

Any repair work we can not complete during routine maintenance we save for our full weekend closure scheduled every summer. If repairs are more pressing, we may need to schedule a closure sooner. These repairs can range in length depending on the type and magnitude of the damage. For example, during the Feb. 25, 2006, closure crews needed the around-the-clock weekend closure because of the heavy equipment required to install the new part. The more lengthy closure allowed crews to safely bring in heavy equipment and work continuously to remove and replace a trunnion beam in the drawspan mechanism that allows the drawspan span to open and close.

What can drivers expect?

The Washington State Patrol works with our crews to ensure the safety of drivers and to make sure cars stay off the bridge during the closure. Eastbound drivers are usually diverted off SR 520 at Montlake Boulevard and westbound drivers are usually diverted off SR 520 at 92 nd Avenue NE. We alert drivers to closures using electronic signs on highways that lead to the bridge, our highway advisory radio, the WSDOT Web site, the 511 traveler information phone line, and media advisories. When the Bridge is re-opened to traffic the electronic signs and highway advisory radio messages are turned off.